Can't paste flatpak items in menu editor

Distribution

CachyOS Kernel 7.1.3-2-cachyos

Package version

6.6.8

Graphics hardware in use

AMD 7900XTX

Frequency

Always

Bug description

When using the menu editor, I am attempting to create a favourites category (that works fine). When I copy an icon from another category, I can usually paste it in my favourites. This doesn't seem to be the case with flatpak apps though. It does create a second copy of the item in the original menu (the one I copied it from) like all the rest, but when I attempt to paste in the favourites category, nothing happens.
I've attached a screenshot of my .local/share/applications directory. You can see some non flatpak icons (Death Stranding, Final Fantasy 7) which are Steam games, and some flatpak files (MakeMKV).

Since the files exist here, I'm not sure why they wouldn't show up in the menu, but I'm far too new to Linux to figure it out on my own.

Steps to reproduce

1. Right-click on the menu icon.
2. Select 'Edit menu'
3. Navigate to a category that has a flatpak application (in my case Sound & Video)
4. Click on the desired icon in the right pane (MakeMKV)
5. Select 'Copy' from the right hand column of buttons
6. Click on another category in the left pane (Favourites in my case)
7. Select 'Paste' from the right hand column of buttons.

Expected behavior

I was expecting that a copy of the MakeMKV icon would appear in the favourites category, but it doesn't. This procedure works with non flatpak applications as far as I can tell, though it creates a duplicate copy of the menu entry in the source category. It seems to be creating the .desktop files in .local/share/applications, but I haven't figured out why the icons don't appear in the menu.

Additional information

No response

Start with the Cinnamon menu editor and reproduce the copy/paste flow using a Flatpak application such as MakeMKV. Inspect the generated .desktop files in .local/share/applications and compare them with the entries that paste successfully. Done means Flatpak items can be copied into another category, including Favourites, without creating an unusable duplicate in the source category.